Fail-safe probe-type thermo-responsive electrical switch device



D. E. PLACE 3,194,927

FAIL-SAFE PROBE-TYPE THERMORESPONSIVE ELECTRICAL SWITCH DEVICE July 13, 1965 2 Sheets-Sheet 1 Filed July 51, 1962 0 FIG. 4

INVENTOR. DONALD E. PLACE ATTORNEY July 13, 1965 D. E. PLACE 3,

FAIL-SAFE PROBE-TYPE THERMORESPONSIVE ELECTRICAL SWITCH DEVICE Filed July 31, 1962 2 Sheets-Sheet 2 A IO 7/ 29' I xfi: 51? Jo ahamgaw A $1 3mm 2 5. 1:; 'QJQ .v i.\ I FIG. 9 fl l F I5 .ls x}? FIG '0 lNVlNTOR A 49 DONALD. E. LACE ATTORNEY United States Patent 3,194,927 FAIL-SAFE PROBE-TYPE THERMO-RESPONSIVE ELECTRICAL SWITCH DEVICE Donaid E. Place, Manstieid, Ohio, assignor to Therm-0- Disc, Incorporated, Mansfield, Ohio, a corporation of Ohio Filed July 31, 1962, Ser. No. 213,767 7 Claims. (Cl. 200-137) This invention relates to a thermo-responsive device and more particularly to switch actuating means for such device which includes a heat sensing probe member adapted to be positioned in the fuel flame of heating appliances, such as furnaces, ranges and clothes dryers.

Although many types of switches have been provided heretofore adapted to operate in response to the presence or absense of a source of heat in a heating appliance such as a furnace, cooking range or clothes dryer, these switches were not particularly reliable in operation over long periods of time. Due to this unreliability and tendency to tail in service, such controls were unsafe for domestic use or as a safety device in the above mentioned appliances. For example, in devices in which a probe was used as a heat sensing element, after extended periods of exposure to the source of heat, the probe would deteriorate or disintegrate and eventually break and thus, fail to actuate the switch in the electric circuit controlling the source of heat to the appliance.

In other cases, the probe will change in physical character to the extent that the switch will fail to operate within the predetermined desired period of time within desired temperature limits. In devices using hi-metal as the flame sensing element, overstress and deterioration of the bimetal has caused failure of the switch actuating elements of the device or resulted in the switch operating Within unsafe or undesirable limits.

It is among the objects of the present invention to provide a new and novel temperature sensing device for actuating a switch in the electric circuit controlling the source of heat in an appliance which is effective to interrupt or open said electric circuit on the absense or re moval of the source of heat surrounding the sensing device or upon a drop in the temperature surrounding the same.

Another object of the present invention is to provide a switch actuating device which will operate within fixed limits of time or temperature regardless of physical changes in the character of the flame sensing element after extended periods of exposure to a flame or other source of heat.

A still further object of the invention is to provide a switch for controlling the flow of current to an electrically operated fuel valve which is actuated in response to a flame sensing element wherein the switch elements are caused to open or close in the event of failure of the flame sensing element.

It is still further object of the invention to provide a switch for a heating appliance which because of its simplicity, economy of construction, and reliability and efficiency of operation, is particularly well adapted as a protective device in controlling the source of heat for such heating appliance.

Another object of the invention is to provide a thermostatic control wherein the switch elements thereof may be operated within a relatively narrow temperature differcntial.

Another object of the invention is to provide a switch having a probe type heat sensing device associated with a frictionally controlled actuating member, wherein upon initial relative movement of the elements of the temperature sensing device the actuating member is caused to operate the switch elements, and further relative move ment of the said elements positions the actuating member for operating the switch element upon initial relative movement of the elements of the sensing device in the opposite direction due to a change in temperature.

These and other objects and advantageous features of the invention, not at this time more particularly pointed out will become apparent as the nature of the invention is better understood from the following detailed description taken in conjunction with the accompanying drawings wherein like reference characters denote corres ponding parts and wherein:

FIGURE 1 is a top plan view of a thermo-responsive device made in accordance with the teachings of the present invention. 7

FIGURE 2 is a longitudinal sectional view on line 22 of the device of FIGURE 1 showing the switch contacts in normal position prior to the application of heat.

FIGURE 3 is an exploded perspective view illustrating the elements of the frictionally controlled actuating assembly. I

FIGURE 4 is a fragmentary sectional view taken along the line 4-4 of FIGURE 1,

FIGURE 5 is a horizontal sectional view taken along the line 55 of FIGUREZ.

FIGURE 6 is a sectional View of the actuating assembly prior to the insertion of the temperature sensing rod,

FIGURE 7 is a sectional view taken along the line 7-7 of FIGURE 2,

FIGURE 8 is a fragmentary vertical sectional View illustrating the relative position of the switch elements and actuating assembly upon an initial rise in temperature.

FIGURE 9 is a fragmentary vertical sectional view illustrating the relative position of the switch elements and actuating assembly at maximum temperature, and

FIGURE 10 is a fragmentary vertical sectional view illustrating the relative position of the switch elements and actuating assembly upon an initial drop in temperature from maximum.

With reference to FIGURES 1, 2 and 4 of the drawings, in its overall assembly, the control device of the present invention embodies a switch proper A which includes a pair of fixed contacts and a mobile contact, adapted to move therebetween, a flame sensing assembly B and an actuating assembly U? which co-ordinates the movements of the elements of assembly B in response to the presence or absence of a source of heat applied to the latter or the influence of temperature changes thereon.

In accordance with the present invention, the switch proper A and the temperature sensing assembly B in themselves are somewhat of conventional construction. The elements of the actuating assembly C which serve to control the movement of the switch contacts in response to movement of the elements of the assembly Bf constitute a novel and improved arrangement for translating the movement which takes place between the elements of assembly B in response to the presence or absence of a source of heat or the reduction in the amount of heat within the chamber surrounding the assembly B. The switch proper A as stated above, of conventional structure, is embodied within a housing 10 which may be of a suitable insulating material, although under certain applications of the switch device, it may be desired to construct the housing of a material which will withstand extremely high temperatures, such being the case when the switch would be placed in close proximity to either the pilot flame or main burner of the heating appliance. The

housing Iii is generally of inverted cup-shaped configura tion having a side wall 11 and an upper end wall 12. The side wall 11 is oifset inwardly adjacent its uppe v. end to form an annular ledge 13. As shown in FIGURES 2 and 4, the housing it) presents a generally cylindrical downwardly facing switch chamber 1 The switch housing 1% is supported by a cup-shaped metal case having a side wall which is hexagonal in its exterior form to receive a suitable wrench for applying the device to an appliance. The lower end of the side wall is turned in laterally to form a horizontal annular wall portion 16. At its lateral inward extremity the annular horizontal wall portion 16 is joined to a a wall of an appliance with which the control is adapted threaded as at 13 to be received in a tapped opening in a wall of an applicane with which the control is adapted to be used. The metal case 15 presents a generally cylindrical interior side wall 19 which is inset laterally at its lower extremity to provide a supporting surface 29 for the end surface of the side wall 11 of the housing lid. The side wall 19 snugly surrounds the outer wall of the housing lit? and terminates in a plurality of tangs 21 which are arranged to be bent over and engage the annular ledge 13 to secure the housing and case in assembled relation.

Mounted within the switch chamber 14 are stationary contact members 22 and 23. The contact member 22 is mounted on the outer free end of an arm 24, the end of which is supported on the lower surface of a spacer sleeve 25. A terminalpost 26 having a headed end Zea extends through the arm 24, spacer sleeve 25, and opening 27 in the end wall 12. of the housing 10 and is secured to a blade terminal 23 positioned on the outer surface of the bottom wall 12 of the housing. Similarly, the stationary contact 23 is mounted on the outer end of an arm 29 which is supported on the lower surface of a spacer sleeve as. A terminal post 31 having a head 31a extends through the arm 29, sleeve 3t), and an opening 32 in the end wall 12. of the housing and is secured to a blade terminal 33 projecting outwardly from the outer surface of the control.

A moveable contact carrying arm 34 (FIGURE 2) carries at its free end mobile contact 35 which presents a rounded surface on the top of the arm 34 to the stationary contact 22 and a similar surface below the arm 34 to the stationary contact 23. The opposite end of the arm 34 is mounted on bushing 36 which is supported on a headed terminal post 37 extending through an opening 38 in the end wall 12 of housing lit and secured to blade terminal 39. The central portion of the end wall 12 is bored and counter-bored as at 40 to provide access to the switch chamber ltd for effecting adjustment of a bumper member 4ll threaded through the mobile contact carrying arm 34. A closure member 42 is seated in the counter-bore of the bore at).

The temperature sensing assembly of the present invention comprises an elongated tube 43, the upper end of which seats within a bore 44 extending axially into the projection 17 of the case 15 from the lower surface thereof. The tube 43 is securely fixed to the case 115 by means of welding as at 45. The tube 43 is preferably made of stainless steel or other suitable metal having a relatively high coefficient of expansion and has mounted therein an elongated rod 4 5 one end of which is welded in the lower end of the tube 43 as at 47 and extends upwardly therefrom through the tube 43 in concentric relation therewith. The rod 46 extends upwardly through an opening 48 into an enlarged cylindrical chamber 49 formed within the projection 17, in which are mounted the elements of the actuating assembly C for translating movement of rod 46 with respect to the tube 43, responsive to temperature changes, to actuate the switch elements. The side wall of the chamber 4-9 is suitably threaded as at St).

The assemblage C comprises a cylindrical clutch housing 51 having an internal bore 52 formed with an inwardly extending flange 52a adjacent its lower end and an outwardly extending peripheral flange 53 adjacent the other end thereof which serves as a restraining collar. The housing 51 receives the upper end of the rod projecting into the chamber 49. Mounted within the lower end of the housing 51 and seated on the flange 52a is a U-shaped spring member 54 which is arranged to encircle the rod 46. When assembled, the inner wall of the housing Sit exerts bending pressure on the legs of the U-shaped member 54 as shown in FIGURE 7 cansing the same to frictionally grip the exterior surface of the rod as therebetween. The spring member 54 is maintained within the clutch housing 51 seated on the ledge 52a by means of a sleeve 55 having the lower exterior surface suitably knurled as at 56, the knurled surface 56 being pressed into the wall surface of the bore 52 of the housing 51 to secure the two elements together. The upper end of the sleeve 55 projects beyond the housing 51 and receives the shank portion 57 of a bumper member 58, the upper surface of which is arranged to engage the lower end of the adjustable bumper member 41 carried by the mobile contact carrying arm 34.

Disposed between the bottom wall of the chamber 49 and the lower surface of the collar 53 of the housing 51 and encircling the same is a coil spring 60 which serves to urge the clutch housing upwardly. The clutch assembly is adjustably mounted within the chamber 49 by means of a bushing 61 having external threads 62 thereon which are received by the threads 50 formed on the chamber wall. The internal shoulder 63 formed on the upper end of the bushing 61 engages the top of the clutch housing 51 and adjustably positions the lower edge surface thereof with respect to the bottom surface of the chamber 49 against the force of the spring 5-9.

In the operation of the device, as shown in FIGURE 2, the switch contacts and elements of assembly C are in the position when the device is under normal room temperature. The mobile contact 35 is maintained in engagement with the fixed contact 22 through upward pressure of the clutch assembly positioned on the rod 46. The gap 65 between the lower end surface of the clutch housing 51 and the bottom surface of the chamber 49 has been predetermined and adjusted by means of the threaded connection between the bushing 61 and the wall of chamber 4?. The bias of the mobile contact arm 34 to separate the contacts 22 and 35 has been overcome by bringing the end of the adjustable bumper member 41 into contact with member 53.

The device is then in condition to be mounted on an appliance, for example, the temperature sensing assembly is inserted into the combustion chamber of a furnace so that the pilot flame of the device plays or impinges upon the assembly. When the assembly B is exposed to the flame of the pilot, the tube 43 will expand lengthwise downwardly as shown in FIGURE 2. Such downward movement of the tube 43) withdraws the rod within the chamber 4Q and moves assembly C downwardly against he upward pressure of spring 60 until the lower end surface of the housing 51 bottoms on the lower surface of chamber 49 (FIGURE 8). This downward movement relieves the pressure on the bumper 41 and the bias of the contact carrying arm 34 breaks engagement between contact 22 and contact 35 and moves the mobile contact 35 into engagement with the fixed contact 23 and closes the circuit to the fuel control valve. The movement of rod 46 will continue due to further expansion of the tube 3 until the elements of assembly C are in the position as shown in FTGURE 9. As appears therein, the rod has moved relative to the U-shaped friction member 54. In the event that the flame of the pilot, or the burner flame should be extinguished or in the event of any unusual drop in temperature surrounding assembly B the tubular member 43 will react quickly and any slight reverse movement due to such reduction in temperature is immediately reflected through the rod 46 and assembly C which thereupon moves upwardly carrying the bumper member 53 into engagement with the lower end of adjustable bumper member 41. The mobile contact arm 34 is moved against the downward bias of the arm and mobile contact 35 is caused to engage fixed contact 22. Continued cooling of the tube 43 and a return to room temperature will eiiect a relative movement between the frictional gripping member 54 and the end of rod in so that the relative positioning of the parts in assembly C will return to that as shown in FIGURE 2 where contacts 35 and 22 are maintained in engagement against the bias of the arm 34 and any slight heating of the tube 43 will cause immediate downward movement of the contact arm 34 and eifect a break between the fixed contact 22 and mobile contact 35.

In the normal use of heat sensing assemblies of the type used in this device, continual impingement of a heating flame on the tube 43 will etfect a change in the physical character of the elements of the assembly, for example, there is a tendency, due to what is known as carbon growth, for the tube to be permanently elongated. Such elongation in the tube would be taken up in the slippage between the friction member 54 and rod 46. Thus, there is always relative movement between the rod and tube upon the flame being removed from the tube or temperature being substantially decreased in the area surrounding the tube and the contraction of the tube would be effective to cause the rod through assembly C to move the mobile contact carrying arm of the switch.

In other instances, the continual impingement of a gas flame upon the tube may cause deterioration of the tube member and eventually brings about a condition where the tube and rod separate. Under such condition, the spring member housed within the assembly C is brought into play to exert pressure through the sleeve member 55 to cause bumper member 58 to exert pressure on the mobile contact carrying arm to close the contacts 35 and 22. Thus, upon the absence of a flame or upon a breakage of the elements of the temperature sensing assembly B or the ineffectiveness of the elements thereof to close the switch, assembly C is effective to open contacts 35 and 23 of the switch mechanism.

While there has been described herein and illustrated in the accompanying drawings, a presently preferred embodiment of the present invention, it is to be understood that various modifications, omissions and refinements which depart from the disclosed embodiment may be adopted without departing from the spirit and scope of this invention as defined in the appended claims.

I claim:

1. A thermo-switch comprising: a housing defining a switch chamber; switch eelments mounted in said chamber including a stationary contact and a mobile contact and a cantilever mounted arm for supporting said mobile contact; a heat responsive probe spaced from said cantilever mounted arm having an elongated tubular member and a rod member mounted within and connected to said tubular member, said tubular member and rod member having different coefficients of thermal expansion; means for translating relative movement between said tubular member and rod member to said cantilever mounted arm including a bushing surrounding an end of said rod member; a frictional member within said bushing connecting the rod member and bushing for movement as a unit; means for adjustably limiting the axial movement of said bushing toward and away from said cantilever mounted arm; and means biasing said bushing in a direction to engage said translating means with said cantilever mounted arm.

2. A thermo-switch comprising: a housing defining a switch chamber; switch elements mounted in said chamber including a stationary contact and a mobile contact; a cantilever mounted arm for supporting said mobile contact; a heat responsive probe spaced from said cantiever mounted arm having an elongated tubular member iii and a rod member mounted within and connected to said tubular member for relative movement toward and away from said cantilever mounted arm in response to changes in temperature; means for translating relative movement between said tubular member and rod member to said cantilever mounted arm including clutch means for connecting the rod member and translating means together 7 Within predetermined axial limits both toward and away from engagement of said translating means with said cantilever mounted arm beyond which the rod member is eifective to move independently of the translating means; and means biasing the translating means towards engagement with said cantilever mounted arm.

3. The device of claim 2 wherein means are provided for adjusting the axial limits of movement of the translating means.

4. A thermo-switch comprising: a housing efining a switch chamber; switch elements mounted in said chamber including a stationary contact and a mobile contact; a cantilever mounted arm within said chamber for supporting said mobile contact; a probe having an elongated tubular member and a rod member mounted within and connected to said tubular member at one end, said tubular member and rod member having different coeiiicients of thermal expansion, the free end of the rod member projecting into said housing for actuating said cantilever mounted arm in response to changes in temperature; means for translating relative movement between said tubular member and rod member to said cantilever mounted arm including a U-shaped friction member surrounding an end of said rod member; means for limiting the axial movement of said rod member and translating means as a unit towards and away from said cantilever mounted arm; and means biasing said translating means towards engagement with said cantilever mounted arm.

5. A thermo-switch comprising: a housing defining a switch chamber; switch elements mounted in said chamber including a stationary contact and a mobile contact; a cantilever mounted arm within said chamber supporting said mobile contact; a heat responsive probe having an elongated tubular member and a rod contained therein connected to said tubular member at one end, said tubular iember and rod member having diiferent coefiicients of expansion, the free end of the rod projecting into said housing for actuating said mobile contact; means for translating relative movement between said tubular member and said rod member to said cantilever mounted arm, said translating means including a sleeve surrounding an translating relative movement between said tubular memsleeve serving togrip the rod member, and a tubular member securing the frictional member within the sleeve and projecting into engagement with the said cantilever mounted arm; andmeans biasing said translating means into engagement with said cantilever mounted arm.

6. The device of claim 5 wherein means are provided for limiting to a predetermined amount the axial movement of the frictional member and rod member as a unit.

7. The device of claim 6 wherein means are provided for adjusting the amount of axial movement of the rod and frictional member as a unit whereby the temperature at which the contacts of the switch are open or closed may be varied.

References Cited by the Examiner UNITED STATES PATENTS 969,848 9/10 Davis 200-437 2,195,649 4/50 Hallenbeck et al 200-l37 2,538,387 1/51 Shidler 200-137 2,814,694 11/57 Moodie 200--137 BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,194,927 July 13, 1965 Donald E. Place J It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 49, strike out "translating relative movement between said tubular mem" and insert instead end of said rod member, a frictional member within said Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A THERMO-SWITCH COMPRISING: A HOUSING DEFINING A SWITCH CHAMBER; SWITCH EELMENTS MOUNTED IN SAID CHAMBER INCLUDING A STATIONARY CONTACT AND A MOBILE CONTACT AND A CANTILEVER MOUNTED ARM FOR SUPPORTING SAID MOBILE CONTACT; A HEAT RESPONSIVE PROBE SPACED FROM SAID CANTILEVER MOUNTED ARM HAVING AN ELONGATED TUBULAR MEMBER AND A ROD MEMBER MOUNTED WITHIN AND CONNECTED TO SAID TUBULAR MEMBER, SAID TUBULAR MEMBER AND ROD MEMBER HAVING DIFFERENT COEFFICIENTS OF THERMAL EXPANSION; MEANS FOR TRANSLATING RELATIVE MOVEMENT BETWEEN SAID 